Photographic hardening bath



Patented July 7, 1925.

UNITED 1 STATES 1,544,936 PATENT "OFFICE.

MILTON B. PUNNET'I, or ROCHESTER, NEW YORK,

COMPANY, or aoorrns'riimivnw YoRK, A conroan'rrou or new YORK.

amoroenarino H nn uINe BATH.

No Drawing.

To all who-m it'vna yconcernr Be it known that I, MILTON B.-PUNNETT, a citiz enof the United States ofAmerica, residing at Rochester, in the county of Mon roe and State of New York, have invented certain new and useful Improvements in Photographic Hardening Baths, of which the following is a full, clear, and exact specification.

hiy invention relates to photographic hardening baths; and to powders adapted when dissolved to constitute such baths; the baths and powders also being capable of addition to a fixing bath to constitute a fixing hardening bath.

A formula that has been in use for many years and which is a very desirable one with certain materials, particularly plates, includes chromium-potassium sulphate, which I shall refer to by, its its popular name, chrome alum, and sulfuric acid. This has, however, the great objection that concentrated sulfuric acid is a chemical which must be handled with careeven by a chemist; and in the hands of a careless or unskilled worker serious accidents may easily occur.

Moreover such care and restrictions are nec-' essary in its shipment and sale that it is impractical to place it on the retail. market or to put it up in a convenient, packaged, ready-to-use forth; so that it is used principally only by the skilled professional photographer who buys his materials in quantity through commercial channels.

The principal object of my invention is to provide a'material in powder form that is the chemical equivalent of this bath and that also has certain addedhardening properties, that can be packed and shipped in convenient form and ready for use by small users or by those who do not care to mix their own chemicals, and which will not be dangerous in shipment or in use. i

This and other obi ects are attained by the use of powdered nitre cake. Nitre cake is a by-product from the manufacture of nitric acid, and is practically valueless in the market. It is obtainable as a hard granular mass and consists of a mixture of sodium sulphate, sodium bi-sulphate and sulfuric acid. The proportions of these vary somewhat in difli'erent batches but for'the purposes which I propose it may be specified in terms of its equivalence to sulfuric acid.

Application filed August 20, 1924. Serial No. 733,232.

Analyses of many different batches of nitre cake show that this varies from 82.6% to 34.5%,i a variation which for my purposes is negligible; q Y

In practice I grind this'mass as obtained into powdered form, and mix it with chrome alum, using two parts of chrome alum to one of nitre cake. The mixture at first be comes moist but upon standing for about a half day it dries to a friable mixture which is easily pulverized. It looses about 8% in weight in this drying and its Weight then becomes constant.

This powder may be packaged in convenient form. The containers must be of material not affected by the powder. Such packages may be distributed through the usual channels and sold by the regular retailers of photographic and chemical products, no unusual care being necessary by such dealers. The user also need not exercise special care in his use of the material.

In use thirty grams of this mixtureis dissolved in four hundred cubiccentimetres of water. customarily this will be added to the regular fixing bath which will contain the following amount of ingredients:

Grams. Sodium thiosulfate 250 Sodium sulfite 20 These chemical will be dissolved in enough water to make a liter when added to the hardening bath. In practice the hardening bath and the hypo bath will be dissolved separately in an indeterminate amount of water .and mixed and then water added to make a liter, the only care necessary being that not too much water is added.-

The sodium sulphate present in the powder acts as a temporary hardener or antiswelling agent and as such is beneficial in its action.

The acid equivalence of the various batches of nitre cake may be determined and the proportion varied if it is found especially high or low. It has been my experience, however, that this is sufficiently constant in the nitrecake as obtained. The acidity of the bath does not have a sharply critical value and may vary within wide limits. In the bath given the acidity is approximately that of a chrome alum-sulfuric ASSIGNOR TO EASTMAN KODAK acid bath when the amount of chrome alum used is eight times by weight that of the C. P. sulphuric acid used.

It is to be understood that the formula given above is by way of example; that a bath of any size may be prepared and'that the proportions used of the several component parts may be varied in their very wide limits, both in compounding the powders and in mixing them in solution.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. The process of preparing a powder suitable for use as a photographic hardening bath that comprises mixing powdered nitre cake and chrome alum, permitting these to dry, and pulverizing the resultant mass.

2. Powdered material capable when dissolved of constituting a photographic hardening bath and comprising chrome alum and nitre cake.

3. Powdered material capable when dissolved of constituting a photographic hardening bath" and comprising substantially two parts of chrome alum and one part nitre cake.

4. Powdered material capable when dissolved of constituting a photographic hardening bath and comprising nitre cake and chrome alum, the acidity of the nitre cake being such that the resulting bath will have an acidity approximately that of a bath in which eight parts of chrome alum and one part of sulfuric acid are used.

5. A hardening bath for photographic emulsions comprising chrome alum and nitre cake. 7

6. A photographic fixing and hardening bath comprising sodium thio'sulfate, sodium sulfite, chrome alum and nit-recake. A

Signed at Rochester, New York, this 14 day of August 1924.

MILTON B. PUNNETT. 

